The goals of the proposed studies are to identified molecular components of neuronal synapses and to determine the role of cell- cell interactions in regulating the assembly and maintenance of this highly specialized structure. Nicotinic cholinergic synapses of the chick parasympathetic ciliary ganglion in situ will be investigated, with major emphasis on the nicotinic acetylcholine receptor (AChR). AChRs will be detected by using monoclonal antibodies to the AChRs of muscle and electric organ that crossreact with neuronal AChRs. The role of pre- and postganglionic interactions in establishing and maintaining the number and ultrastructural distribution of AChRs in surface and intracellular pools in the early developing neurons will be determined using biochemical and immunocytochemical techniques. The regulatory consequences of the disruption of cell-cell interactions will be examined in chick ciliary ganglion neurons at late stages of development when the size of the internal AChR pool appears to be substantially reduced. The regulation of a distinct non-synaptic cholinergic membrane component, the alpha- bungarotoxin binding component, will be compared to AChRs in the developing neurons. Affinity purified antibodies to specific postsynaptic and extracellular matrix components will be used to identify other neuronal synaptic components. The role of cell-cell interactions in establishing and maintaining the levels and spatial arrangement of the components on the neuronal surface will be determined. The independent roles of activity, neuropeptides and neurotrophic factors in the regulation of synaptic and non-synaptic components will be assessed and compared to the regulatory consequences of cell-cell interactions in the ganglion at various developmental stages. The persistence of AChRs and other identified synaptic components after denervation will be used to examine the specificity of the site of reinnervation on the denervated neuron surface in situ and in culture at the ultrastructural level. It is expected that unique regulatory mechanisms involved in the assembly, maintenance and modulation of function at neuronal synapses will be identified. These studies will also increase our knowledge at a molecular level of the neuronal response to damage and the degree of specificty associated with the reestablishment of neuronal synaptic connections.